High-frequency lamp circuit for copying apparatus

ABSTRACT

A high-frequency power supply for the light source of a xerographic-type copying machine in which power from a normal 5060-cycle AC input is rectified and regulated to provide a constant current or constant voltage DC input to a high-frequency oscillator-inverter providing output power at a frequency in the order of 20,000 c.p.s. or above to a light source comprising one or more gaseous-type lamps. In a modified circuit the DC input to the inverter is regulated by a solid-state chopper controlled by a magnetic amplifier pulsed by a free-running multivibrator and modulated by the input current.

United States Patent [72] Inventors Boleslaw C. Biega Deerfleld; Bodo M. Wolflramm, Clarendon Hills, both of III.

[21] Appl.No. 811,831

[22] Filed Apr. 1, 1969 45] Patented Nov. 9, 1 97 l [73] Assignee Sola Basic Industries, Inc.

Milwaukee, Wis.

[54] HIGH-FREQUENCY LAMP CIRCUIT FOR COPYING APPARATUS 6 Claims, 2 Drawing Figs. [52] US. 315/105, 315/101, 315/206, 315/224, 315/260, 315/279, 3 l S/DIG. 7, 328/33 [51] Int. Cl H05b41/29, HOSb 41/391 [50] Field ofSearch 3l5/97,98,

100, 101,105, 174, 194, 200, 205, 206, 209, 219, 224, 246, 260, 279, 287; 331/109; 328/13, 28, 3l-33;307/26l,264; 323/l,2,4

[56] References Cited UNITED STATES PATENTS 2,923,856 2/1960 Greene et a]. 315/138 3,297,954 1/1967 Wiley 331/52 FOREIGN PATENTS 1,149,111 5/1963 Germany 315/100 Primary Examiner-Roy Lake Assistant Examiner-E. R. LaRoche Attorney-Smythe & Moore ABSTRACT: A high-frequency power supply for the light source of a xerographic-type copying machine in which power from a normal 50-60-cycle AC input is rectified and regulated to provide a constant current or constant voltage DC input to a high-frequency oscillator-inverter providing output power at a frequency in the order of 20,000 c.p.s. or above to a light source comprising one or more gaseous-type lamps. In a modified circuit the DC input to the inverter is regulated by a solid-state chopper controlled by a magnetic amplifier pulsed by a free-running multivibrator and modulated by the input current.

PATENTEuunv 9 l9?! SHEET 1 UF 2 ATTORNEYS PATENTEDNUV 9 191:

SHEEI 2 OF 2 oth ATTORNEY$ HIGH-FREQUENCY LAMP CIRCUIT FOR COPYING APPARATUS This invention relates to copying apparatus and more particularly to a supply source for the lamps of such apparatus, especially of the xerographic or similar type.

Reproduction machines of the xerographic type are well known, one such being a machine sold under the trademark Xerox, a trademark of the Xerox Corp. One of the disadvantages of the prior art machines, however, has been the flicker induced in the copies by the frequency of the supply source for the lamp. Such machines, furthermore, frequently provide an undesirable audible hum, and require fairly expensive components in the ballast circuit for the light source.

One of the objects of the present invention is to provide an improved circuit for supplying power to the lamps of copying apparatus, especially of the xerographic type.

A further object is the provision of an improved power supply for operating the lamps of reproduction machines at a high frequency so as to eliminate flicker in the reproduced copies.

A further object is to provide a power supply for operating the lamps of reproducing apparatus at a frequency above the audible range, for example, in the order of 20,000 c.p.s. or higher. 7

A further object is to provide a power supply for copying apparatus which eliminates hum or other audible noises and effects economy in design and operation by utilizing less expensive and more emcient components.

A further object is the provision of a power source for the gaseous-type lamps of copying machines in which a low-loss solid-state regulator replaces the usual high-loss ballast choke as a current limiter for the negative resistance characteristic of the lamps.

A still further object is to provide a power source which delivers square wave pulses of constant magnitude to the lamps of copying apparatus thereby to maintain a constant level of light output during the entire time that the lamps are on.

In one aspect of the invention, power from a normal 50-60- cycle AC power line or the like is fed to a filtered rectifying bridge providing a filtered DC input to a constant current or constant voltage regulator. The output of the regulator is fed to an oscillatoninverter producing a square wave output at a frequency above audible frequency. The output of the inverter is fed to one or more lamps of the fluorescent or gaseousdischarge-type thereby to produce a constant, flicker-free light output for the light source of a copying apparatus such as the xerographic type.

In a second aspect, the regulator for feeding constant current DC to the inverter comprises a solid-state chopper controlled by a magnetic amplifier pulsed by a free-running multivibrator and modulated by output current feedback.

The above and other objects, advantages and features of the invention will be apparent from the following description taken in conjunction with the accompanying drawings which illustrate exemplary embodiments of the invention.

In the drawings:

FIG. I is a schematic wiring diagram illustrating one form of the invention; and

FIG. 2 is a schematic wiring diagram illustrating a modified form of the invention.

Referring to the drawings and more particularly to FIG. 1, there are shown input terminals 10 and 1] adapted for connection to any suitable source of ll5-volt, 5060-cycle AC power. The terminal is connected by line [2 to the input terminal 13 of a rectifying bridge 14. The terminal 15 of the bridge is connected through line 16 to the input terminal 11. A resistance 17 and a capacitor 18 provide for filtering the output of the bridge 14. A constant current regulator 19 indicated generally by the dashed lines 19A is connected to the output terminals 20 and 21 of the bridge 14. Variable resistance [98 can be used to adjust output current. Zener diode or reference means 19C is used to provide a feedback signal to provide a closed loop operation to series-regulating transistor 22. The

regulator 19 may be of any desired type but as shown in FIG. 1 comprises temperature-compensated series transistor 22.

g The output of the regulator 19 is fed to the capacitor 23 of an oscillator inverter 25 indicated generally by the dashed lines 24. The inverter 25 may be of any desired type but, as shown in FIG. 1, includes transistors 26 and 27, an output transformer 28 having primary windings 29 and 30 and feed back winding 31 and a feedback transformer 32 connected by the lines 33 and 34 and a resistance 35 to the winding 31. The inverter 25 is designed to operate at a high frequency in the order of 20,000 c.p.s. or more and provides a square wave output of constant current amplitude. This output isfed by the secondary 36 of transformer 28 to the tenninals 37 and 38 of a fluorescent gaseous lamp 39 comprising the light source of any well-known copying machine. windings 40 and! on the transformer 28 energize the filaments 42 and'43 of the lamp 39, and a small step-up voltage through the secondary 36 of transformer 28 in conjunction with a grounded plate provides for quick starting of the lamp as a result of the highfrequency input to the lamp. The constant current, square wave output of the converter 25 effects constant light output from the lamp 39 during the entire time that the lamp is on. A switch 45 shown in open or standby position operated in any well-known manner provides for connecting the lamp 39 to the inverter 25.

Referring now to FIG. 2 of the drawings,'there is shown a more efficient constant current regulator 46 indicated generally by the dashed lines 47. As shown, this regulator comprises a free-running multivibrator 48 of a well-known type fed by a filtered rectifying bridge 49 connected by lines 50 and 51 to the terminals 52 and 53 to a suitable source of AC power. Reference means 49A is similar to reference means 19C of FIG. 1. An output transformer 54'ofthe mul tivibrator 48 magnetically couples the multivibratortoa magnetic amplifier 55 to provide square wave pulses of a'frequency in the order of 2,000 c.p.s., for example, to-the magamp 55 biased by a winding 56 or a frequency to avoid beat frequen cies. The output of the magamp 55is fedthrough a rectifying bridge 56 to the transistors 57 and 58 of a chopper59. A variable resistor 56B is provided similar ,to 19B of FIG. I. The chopper 59 is connected in series with the output'lines 63 and 64 of a rectifying bridge 60 connected to the AC input terminals 52 and 53 and filtered by the resistance 61 and capacitor 62. The output of chopper 59 is filtered by an inductance 63A and capacitor 65 and is fed to the oscillator-inverter 66 by means of a line 67 and a feedback winding 68 on the mag netic amplifier 55 which modulates the pulse width delivered to the transistor 58, thereby to provide a constant current to inverter 66.

The inverter 66 is of a well-known type and includes the transistors 79 and 80 and an output transfonner Bl. The transformer 81 is connected through a switch 82 shown in open or standby position, and lines 83 and 84 to a pair of fluorescent lamps 8S and. windings 87, 88, 89 and 90 on the transformer 81 energize the filaments 91, 92, 93 and 94 of the lamps 85 and 86. A winding 95 on the transformer 81, connected in series with a capacitor 96 and resistance 97, provides a starting voltage for the lamps 85 and 86. As in HG. l, the transformer 81 provides a square wave, constant current input to the lamps 85 and 86.

While certain embodiments of the invention have been shown and described, changes and modifications may be made as defined within the scope of the appended claims,

What is claimed is:

1. In a circuit for supplying power to at least one gaseous discharge lamp means for energizing copying machines or the like apparatus, the combination including input means for connection with a source of AC having normal power line frequency, rectifying means for converting said AC into DC to provide a DC output, filtering means connected with said rectifying means, series regulator means in said DC output operating in a closed loop having a DC reference means providing a feedback, so that in the standby mode of the lamp means, power supply filament voltage at open circuit lampstarting voltage is provided and said voltages are automatically decreased to operating voltages for said gaseous discharge lamp means when switched from standby to operating mode, inverter means connected to said series regulator means and operating above audible frequency and including an output transformer connected to said inverter means, said inverter means providing a substantially square wave to said gaseous discharge lamp means, and connecting means from said output transformer to said gaseous discharge lamp means.

2. A circuit as claimed in claim 1 including means wherein said reference means includes manually adjustable means to adjust the luminous intensity of the gaseous discharge lamp means.

3. A circuit as claimed in claim 1 including a magnetic-amplifier-driven chopper in said series regulator, said magnetic amplifier having an isolated feedback and bias current circuit means providing the regulation function.

4. A circuit as claimed in claim 3 wherein said series regulator includes a solid-state chopper and means for controlling the pulse width operation of said chopper.

5. A combination as defined in claim 4 in which said means for controlling said chopper includes a multivibrator magnetically coupled to said magnetic amplifier, and a feedback winding on said magnetic amplifier connected in series with the output from said chopper.

6. A combination as defined in claim 5 wherein said multivibrator operates at a different frequency from the inverter to avoid beat frequency oscillations.

at a a a t 

1. In a circuit for supplying power to at least one gaseous discharge lamp means for energizing copying machines or the like apparatus, the combination including input means for connection with a source of AC having normal power line frequency, rectifying means for converting said AC into DC to provide a DC output, filtering means connected with said rectifying means, series regulator means in said DC output operating in a closed loop having a DC reference means providing a feedback, so that in the standby mode of the lamp means, power supply filament voltage at open circuit lamp-starting voltage is provided and said voltages are automatically decreased to operating voltages for said gaseous discharge lamp means when switched from standby to operating mode, inverter means connected to said series regulator means and operating above audible frequency and including an output transformer connected to said inverter means, said inverter means providing a substantially square wave to said gaseous discharge lamp means, and connecting means from said output transformer to said gaseous discharge lamp means.
 2. A circuit as claimed in claim 1 including means wherein said reference means includes manually adjustable means to adjust the luminous intensity of the gaseous discharge lamp means.
 3. A circuit as claimed in claim 1 including a magnetic-amplifier-driven chopper in said series regulator, said magnetic amplifier having an isolated feedback and bias current circuit means providing the regulation function.
 4. A circuit as claimed in claim 3 wherein said series regulator includes a solid-state chopper and means for controlling the pulse width operation of said chopper.
 5. A combination as defined in claim 4 in which said means for controlling said chopper includes a multivibrator magnetically coupled to said magnetic amplifier, and a feedback winding on said magnetic amplifier connected in series with the output from said chopper.
 6. A combination as defined in claim 5 wherein said multivibrator operates at a different frequency from the inverter to avoid beat frequency oscillations. 